Fuel cells electrochemically convert fuels and oxidants to electricity, and fuel cells can be categorized according to the type of electrolyte (e.g., solid oxide, molten carbonate, alkaline, phosphoric acid, or solid polymer) used to accommodate ion transfer during operation. Moreover, fuel cell assemblies can be employed in many (e.g., automotive to aerospace to industrial) environments, for multiple applications.
A Proton Exchange Membrane (hereinafter "PEM") fuel cell converts the chemical energy of fuels such as hydrogen and oxidants such as air/oxygen directly into electrical energy. The PEM is a solid polymer electrolyte that permits the passage of protons (i.e., H.sup.+ ions) from the "anode" side of a fuel cell to the "cathode" side of the fuel cell while preventing passage therethrough of reactant fluids (e.g., hydrogen and air/oxygen gases). Some artisans consider the acronym "PEM" to represent "Polymer Electrolyte Membrane." The direction, from anode to cathode, of flow of protons serves as the basis for labeling an "anode" side and a "cathode" side of every layer in the fuel cell, and in the fuel cell assembly or stack.
Usually, an individual PEM-type fuel cell has multiple, generally transversely extending layers assembled in a longitudinal direction. In the typical fuel cell assembly or stack, all layers which extend to the periphery of the fuel cells have holes therethrough for alignment and formation of fluid manifolds that generally service fluids for the stack. As is known in the art, some of the fluid manifolds distribute fuel (e.g., hydrogen) and oxidant (e.g., air/oxygen) to, and remove unused fuel and oxidant as well as product water from, fluid flow plates which serve as flow field plates for each fuel cell. Also, other fluid manifolds circulate coolant (e.g., water) for cooling.
As is known in the art, the PEM can work more effectively if it is wet. Conversely, once any area of the PEM dries out, the fuel cell does not generate any product water in that area because the electrochemical reaction there stops. Undesirably, this drying out can progressively march across the PEM until the fuel cell fails completely. So, the fuel and oxidant fed to each fuel cell are usually humidified. Furthermore, a cooling mechanism is commonly employed for removal of heat generated during operation of the fuel cells.
Flow field plates are commonly produced by any of a variety of processes. One plate construction technique, which may be referred to as "monolithic" style, compresses carbon powder into a coherent mass. Next, the coherent mass is subjected to high temperature processes which bind the carbon particles together, and convert a portion of the mass into graphite for improved electrical conductivity. Then, the mass is cut into slices, which are formed into the flow field plates. Usually, each flow field plate is subjected to a sealing process (e.g., resin impregnation) in order to decrease gas permeation therethrough and reduce the risk of uncontrolled reactions. Typically, flow field channels are engraved or milled into a face of the rigid, resin-impregnated graphite plate. In order to effectively distribute reactant fluid and/or humidification fluid for the PEM, it is desirable that the flow channels remain as open and unclogged as possible. As will be understood by those skilled in the art, it is further desirable that a mechanism be included in the fuel cell stack for occupying (e.g., longitudinal) space which can develop after initial assembly of the layers, to promote electrical conductivity and/or fluid(s) service therethrough.
Another known flow field configuration places a tridimensional network mattress with spiked surfaces, formed by metal-wire fibers, between a bipolar plate and an electrocatalytic electrode, which is in turn adjacent to an ion exchange membrane. The mattress acts as distributor for the reactants and products, in addition to providing deformability and resiliency in the electrochemical cell. The bipolar plate itself has planar surfaces without continuous or complete flow channels, and is formed from aluminum or other metal alloys capable of forming oxides. Such a design is disclosed in U.S. Pat. No. 5,482,792 to Faita et al. (entitled "Electrochemical Cell Provided With Ion Exchange Membranes and Bipolar Metal Plates," issued Jan. 9, 1996, and assigned to De Nora Parmelec S.p.A.) and U.S. Pat. No. 5,565,072 to Faita et al. (entitled "Electrochemical Cell Provided With Ion Exchange Membranes and Bipolar Metal Plates," issued Oct. 15, 1996, and assigned to De Nora Parmelec S.p.A.). A shortcoming of this design is the excessive material resource expense and weight, as well as the space consumption, in providing the mattress and plate. Another shortcoming is the non-uniformity in the fluid and pressure distributions resulting from the mattress.
Thus, a need exists for a mechanism for maintaining open and unclogged, flow channels of a flow field plate in a fuel cell assembly. A further need exists for such a mechanism which enhances conductivity through the fuel cell assembly. An additional need exists for the mechanism to promote stability and support for the fuel cell assembly.